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10th International Rainwater Catchment Systems Conference
"Rainwater International 2001"
Mannheim, Germany - September 2001

Section 4: Rainwater Catchment in Agriculture

Paper 4.21

Water Conservation Techniques on Small Plots in Semiarid Areas to Increase Sunflower Yields

J.J. Botha, J.J. Anderson, P.P. van Staden, L.D. van Rensburg
ARC - Institute for Soil, Climate and Water
Private Bag X01
Glen, 9360
South Africa


Dryland crop production in South Africa is liable to short seasonal or long annual droughts that lead to uncertain yields and frequent crop failures. There is a great need therefore to quantify risk and improve the rainfall use efficiency (PUE) by employing appropriate production techniques. A large area east of Bloemfontein (750 000 ha), sometimes termed the "resettlement area", has been earmarked for developing farmers. The area is marginal for crop production. There are two reasons for this (a) low and erractic rainfall (520 mm to 600 mm per annum) and (b) dominantly clay soils on which the PUE is low due to high runoff (R) and soil evaporation (Es) losses. The production techniques developed by the ARC-Glen team (Hensley, Botha, Anderson, van Staden & du Toit, 2000) that combines the advantages of water harvesting, no-till, basin tillage and mulching in the basins on high drought risk clay soil reduced total runoff to zero and Es considerably. The main water loss is considered to be Es. Soil movement from the runoff strip into the basins however may be a problem in the long-term in the relation to sustainable crop production. The question that needs to be answered can be stated as follows: Can an appropriate water conservation production technique be developed which can decrease Es to a reasonable level, and which is also sustainable?
It is hypothesised that mulch (organic or stone) on the runoff area will depress Es and soil movement and therefore promote higher yields and sustainability.

Significantly higher sunflower yield were obtained with the WHB technique compared to the Con technique, due to a reduction in runoff. WHB-OS and WHB-SO techniques also gave higher yields than the WHB-OB technique because of the reduction in Es. The experiment has shown that the losses, R + Es, play an important role in crop production. Although more research is needed, results have shown that with the WHB-OS and WHB-SO production techniques, crop production with reasonable high yields are possible on these high drought risk clay soils. The new technique could lead to a reduction of poverty or serious financial problems resulting from crop failures.

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